In fairness, a President's authority to fire some cruise missiles into another country without checking with Congress has become a hazy area of Constitutional law in modern times. It's true that under Article I, Section 8, Congress has the power to declare war, tax and spend for defense, and provide for our armed forces.

On the executive side, however, the Constitution simultaneously names the President as the "Commander in Chief of the Army and Navy of the United States," who must, to the best of his ability "preserve, protect and defend the Constitution of the United States."

JUST WATCHED

Rand Paul on opposing Syrian attack

MUST WATCH

Rand Paul on opposing Syrian attack10:30

Beyond the Constitution, federal legislation and even international law arguably define the executive's power. The War Powers Resolution (WPR) of 1973 limits the constitutional powers of the President as commander in chief to engaging in "hostilities" only when there is: (1) a declaration of war, (2) specific statutory authorization, or (3) a national emergency created by attack on the United States, or its military.

Read More

While a "humanitarian" reason for attacks certainly seems like a laudable moral objective, this might not be a valid reason to attack under domestic law. Internationally, the UN Charter appears to explicitly prohibit all foreign military intervention without Security Council authorization, unless taken in self-defense. The President has an easy way around these legal constraints, however.

He can just do whatever he wants.

If he insists that he has the authority, then Congress will either back him up, or at least not argue with him. The courts will probably stay out of it, too.

How can he order air strikes in apparent defiance of the Constitution, federal and international law? Simple: the other guys did it.

Other presidents have launched attacks on sovereign nations for humanitarian reasons. Bill Clinton did it in Kosovo, and justified intervention in Haiti and Bosnia. Barack Obama initiated military action in Libya, and threatened to do it in Syria, too.

Both Clinton and Obama took the position that Congressional authorization is not required if the military action does not rise to the level of "war".

The Clinton administration justified the President's use of force abroad without congressional approval as long as there was some "compelling national interest"—whatever that is. It's likely no coincidence that Thursday night, a U.S. official reportedly insisted that President Trump has the power under the Constitution to use force overseas to defend the U.S. national interest.

JUST WATCHED

Kaine: No legal justification for Syria strike

MUST WATCH

Kaine: No legal justification for Syria strike01:20

It's pretty amazing when you think about it: firing 59 Tomahawk missiles at a military base in a sovereign nation might not be an "act of war," constitutionally. The framers didn't have cruise missiles, so they expressed no opinion in the Constitution on whether using them to strike targets in other countries a thousand miles away constituted "war." But the lawmakers of the 18th century were definitely familiar with the concept of a "limited war," military campaigns of supposedly limited duration, but more than a one-and-done offensive. It's hard to imagine that they would have considered any strike — missile or cannonball — to be not an act of war requiring congressional authorization.

Some individual members of Congress have complained aloud that this strike might be illegal; others — Democrats — are saying that Trump should have asked for permission first. Ultimately, those denouncements may be more form than substance. As one scholar has argued, the "current political system gives the President incentives to overreach, Congress incentives to acquiesce, and the courts incentives to defer" when it comes to limited military actions abroad.

History has shown us that, in spite of the critical voices, Congress will probably either authorize after the fact, or just do nothing. The courts don't want any part of it either. In the past, they have dismissed cases brought by members of Congress who claimed that a President's use of military force abroad violated federal law and the Constitution.

Sometimes evaluating an action through the lens of the law seems trivial when we are confronted with images of children being gassed by their own government. But while horrific, those actions are definitely not an attack against the United States or its troops.

Even so, Trump cannot be expected to adhere to legal limitations that prior executives have simply ignored, or conveniently re-interpreted. The Constitution vests Congress with the exclusive power to declare war. It seems that in modern times, the President has the power to determine what the "national interest" is, and when it requires the occasional flurry of missiles into a sovereign nation's military airfield.

We may have entered an era where a humanitarian crisis abroad — along with a history of defiance -- authorizes the flouting of federal law and the Constitution — as long as it's not "war."